A ponnuki is worth thirty points

  Difficulty: Intermediate   Keywords: Shape, Proverb
[Diagram]

Ponnuki

The proverb 'A Ponnuki is worth thirty points' tells us that the ponnuki shape in this diagram is often very valuable.



Especially when played in the center, or some other open space, a ponnuki can exert influence in all directions. The number 30 here is of course just a manner of speaking - what is important is that it is large. One needs a very good reason to allow one's opponent to get one.

[Diagram]

Tortoise shell

Even better than the ponnuki is the tortoise shell in this diagram, where two stones have been captured.



By analogy with the ponnuki proverb, some say that this shape is worth 60 points. Again, one should not take this number too literally, but whatever the value of this position is, it is huge.

-- Andre Engels


SnotNose I noticed that in professional games ponnukis occur with surprising frequency, particularly in the middle game. What I mean is that when I review pro games, I often see situations in which I would play out of the atari of a single stone but the pro does not. Were it possible to search games by pros and amateurs and count ponnukis, I wonder if there are more in the former than in the latter. Or maybe it is a kyu/dan distinction. Bottom line: allowing a ponnuki is not automatically bad. As with many aspects of go: it depends on the situation.


The value of a ponnuki depends on whether it appears in the fuseki, the middle game, or the EndGame. Usually the later the game, the less valuable the ponnuki is. The reason for this is that a ponnuki is thick, which means it is hard (or impossible) to attack a ponnuki. This is because ponnukis can easily be turned into living groups, as they have a rich potential for creating eyes.

A thick shape has strong influence and thus a ponnuki can later be used for attack, for building territory, or as safe haven for retreating invasion stones. By now you should see why ponnukis are worth 30 points.

--ArnoHollosi


BillSpight: I suspect that the 30 points in the proverb comes from the old estimate that a stone is worth 10 points. True, there are four stones in a ponnuki, but presumably the shape was formed by capturing one stone, which makes the net number of stones three. If no mistake has been made by the maker of the ponnuki early in the game, 30 points may be an underestimate.

You don't just see ponnuki floating around. E. g.,

[Diagram]

Ponnuki not so lucky

Black is obviously overconcentrated. Bob Myers: But this is not a ponnuki. It's just a diamond shape.


What the proverb does is warn against this kind of thing.

[Diagram]

Not worth it

Black has connected, but at the cost of allowing a ponnuki. The ponnuki is stronger than it looks.

[Diagram]

Tewari

If we regard the three pairings BC/WC as roughly equal (although slightly favorable for Black), the ponnuki stone WS is almost a free move.

Sebastian: I don't get this. How can you say the ponnuki is strong here? If W doesn't fill it, B can take it and the outcome depends on who has the better ko threats. If B wins the ko fight and fills then the ponnuki is shattered in three pieces with nice cutting points. If W does fill it, it's not a ponnuki anymore and the southern side rather resembles two empty triangles - W2 and W4 look superfluous. Moreover, it may even be gote if the situation is such that B doesn't have to worry about its cutting points. -- 2003-09-24

Bill: You are right that White is in no hurry to fill the ko. By the same token, Black should be in no hurry to take and win it. If he does, White can regard the remaining three stones lightly. They become easy to throw away. While Black takes and wins the ko, White will make profit somewhere else.

Charles Agree with Bill. Black already has two stones more than White here (local tally BB, noting that one black stone has been captured). If Black takes and then fills the ko, that becomes BBBB.

Sebastian: Thanks for both your replies. Bill's clarification that both are in no hurry shows that there is some temporary stability in the position, but I still don't see why the ponnuki is worth 30 points (or even anywhere close).

Charles, I don't see how you get to BB. Taking the interloper as given is a convention (because the original context of "warn[ing] against this kind of thing" was examining Black's choices.) From then on the sequence is B1,W2,B3,W4,B5,W6,B7, which reduces to B. Or does local tally add special points for taking prisoners?

Charles Yes - useless without that. Seven black, five white stones.

[Diagram]

Where are White's 14+30 points?

Black has built a nice territory, so W has to have something in exchange, presumably it's influence. But White's shape is anything but an iron wall, and with 2 more investments (i.e. if W tenukis twice to throw away the stones), Black can crush White's influence. OTOH, turning this into solid territory for White takes probably even more local tally investments.

Who can find the mistake in my reasoning? Thanks!

Bill: Elementary oversight: To say that the White ponnuki is worth 30 points says nothing about how much the Black stones are worth. In fact, since Black has invested 6 stones to White's 4, you should expect Black to have a local advantage. Even though Black's stones are not as efficient as White's, I would expect Black's advantage to be at least 20 points.
Estimating the value of thickness is not easy. This proverb gives a very rough rule of thumb. :-)

Sebastian: Thanks! Now I think I got it. So you could roughly say: If the ponnuki were not there then Black would have outside influence worth a lot, and with it it has hardly any - about 30 points less. Correct?

Bill: Well, it isn't just that Black does not have a strong wall, radiating influence. White's ponnuki is strong, although not nearly as strong as a ponnuki standing alone. Also, such a comparison is in a way unfair to Black, who would not build such a wall except in response to White's plays. Tewari is the best way to think about these things.
And don't get hung up on the number 30. It is a very rough estimate. The main point is that thickness is usually larger than it looks, perhaps a lot larger, especially early in the game. :-)

BTW, what is the difficulty of this page? If it's "advanced" then I will apologize and tenuki to my playground. ;-)

John F. It is my experience that this is one of the best benchmark positions around: understanding the explanation given (I agree with what Bill and Charles say) seems to be a sharp marker for a higher dan amateur. My experience is that even European 1-dans don't get it, but Charles has much more experience as a teacher. Charles: do you agree and if so at what level do you put it?

Bill: To understand this proverb and the explanation, you probably have to be a dan player. But I think you only have to be a middling kyu player to apply it fairly well. If most of them do not, I suspect it's from lack of trying. It takes a certain amount of faith. :-)

Charles I marked the page as 'Intermediate'. The proverb of course has exceptions: but a mid-kyu player will benefit from not handing the opponent ponnukis (particularly in this example position).

[Diagram]

White forces

It might help to dramatise the situation, to add W1 and W3 as forcing plays here: Black can hardly resist.



[Diagram]

Reference diagram

It might also help to look at a sequence where Black builds up in the centre with B1. Here again the local tally ends up BB: but the BC and BS stones are now working to build on a large scale in the centre.

Sebastian: Wait a minute - what happened to the white interloper?



Charles This sequence is sente for Black, the previous result is sente for White. You are supposed to notice how 'forced down' Black is, in the first of the two diagrams.


Kungfu: A comment on what Bill said above: You are right, but the truth is that ponnuki is worth 30 points, but White's framework is worth more especially since it's White's move. Yet I don't know if I would say the game wasn't even.

[Diagram]

19x19 diagram

Something like this, or a variation, is given in a book by Otake Hideo as being an even situation.



It's Black's move now. It is given in his book "Opening Theory made Easy" under the section title "A ponnuki is worth 30 points". I have played and won about 40% of my games when using this "fuseki", against players of even strength. I actually reccomend it for Black to try this at least once, to help point out some faults in Black's whole board thinking against players of equal strength.

Bill: If you have lost about 60% of your games with that fuseki, then you have given up the value of almost one move.

DaveSigaty: Note that ponnuki is not a shape in Japanese. It is the act of capturing an enemy stone with four of your own ("pon" is the sound made by the final stone that removes - "nuki" - the enemy stone -- according to the Go glossary at the back of Yamabe's Gendai Joseki Jiten). As Bill mentioned above, the captured stone reduces the net stone count to just three. Similarly the tortoise shell shape is formed by only four stones net as long as two white stones are captured.

Compare the following two continuations. If the second is equal then the first must be significantly to Black's advantage.

[Diagram]

A center ponnuki



[Diagram]

A center diamond



Kungfu comments: Thanks, Dave. Very interesting point. However I view the result as not too much different, since in 1 above, White has sente, while in 2, Black has sente.

Did White give up a stone for sente, and if so, is it worth the difference in board position in such a game?

Kungfu, consider carefully what you are saying. Look at the last diagram above after Black plays B7. Is it true that you see not too much difference between:
  • White playing at W8 with Black to play next (= the situation in the diagram), and
  • White passing, Black playing at W8 with White to play next (= the situation in the previous diagram)?
In other words, you view the situation as not too much different whether you play or pass for your turn? :-) Dave




[Diagram]

And some kikashi to screw it up

lavalyn: Kikashi is a good thing and I think this shows fighting spirit.

Bill: I think the right term for this is approaching strong stones. It may show fighting spirit, but it is not a good thing.
[Diagram]

White ponnuki

-exswoo:I think it's worth noting that a White ponnuki situation here would give White sente even though it's similar to the diagram above. :)



[Diagram]

Add a stone and throw them away

lavalyn: As with this. White now has two cutting points to deal with.


[Diagram]

Two connected ponnukis

Warp: How about two connected ponnukis?

In a recent game between Lee ChangHo (B) vs. Lee SeDol (W) this position happened. How much is it worth? :)


This is a copy of the living page "A ponnuki is worth thirty points" at Sensei's Library.
(OC) 2004 the Authors, published under the OpenContent License V1.0.
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